Three-piece, wound golf balls with balata covers are preferred by most expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer.
In contrast, amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hardness of the ionomer cover, these balls are almost impossible to cut, but they also have a very hard "feel", which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball and the durability of a solid, two-piece ball, but none have succeeded totally. For example, U.S. Pat. No. 4,274,637 to Molitor discloses two- and three-piece golf balls having covers completely or partially formed from a cellular polymeric material to improve backspin, but does not provide any examples that compare the spin rates of the disclosed golf balls with those of prior art balls.
U.S. Pat. No. 5,002,281 to Nakahara et al. discloses a three-piece solid golf ball having an ionomer cover and a solid core consisting of a soft inner core surrounded by a hard outer shell, where the difference in the hardness of the two parts of the core is at least 10 on the JIS-C scale.
Similarly, U.S. Pat. No. 4,781,383 to Kamada et al. discloses a solid, three-piece golf ball, having an ionomer cover and a core with inner and outer layers, where the inner layer has a diameter of 24 to 29 mm and a Shore D hardness of 15 to 30, and the outer layer has a diameter of 36 to 41 and a Shore D hardness of 55 to 65.
European Patent Application 0 633 043 discloses a solid, three-piece golf ball with an ionomer or balata cover, a center core, and an intermediate layer. The center core has a diameter of at least 29 mm and a specific gravity of less than 1.4. The intermediate layer has a thickness of at least 1 mm, a specific gravity of less than 1.2, and a hardness of at least 85 on the JIS-C scale.
Blending a polymer and an ionomer is one approach which has been used in forming golf ball covers, and thus golf balls, with improved properties. One such combination is disclosed in U.S. Pat. No. 4,858,924 to Saito, which teaches the use of a thermoplastic resin with a flexural modulus of 1,500 to 5,000 kg/cm.sup.2 blended with an ionomer to form the cover of a golf ball. Particularly, polyamide elastomer, urethane elastomer, styrene-butadiene copolymer elastomer and polyester elastomer are said to be preferred when used alone or blended with a matrix resin, that is, another like flexible thermoplastic resin. The polyester elastomers are said to include block copoly(ether-esters), block copoly(lactone-esters) and aliphatic and aromatic dicarboxylic acid copolymerized polyesters. However, the Saito patent does not teach the use of the polyester, poly(trimethylene terephthalate), in a golf ball cover.
In pigmented golf ball covers, the color of the cover is enhanced by the use of optical brightener in combination with a pigment system. The use of an optical brightener is desired especially when the cover material is not white in appearance. By incorporating an optical brightener in the cover, the need for a supplemental paint coating can be reduced or eliminated. U.S. Pat. No. 4,679,795 to Melvin et al. discloses blends of optical brighteners with the following golf ball materials: polyolefins and their copolymers; polyurethanes; polyamides, polyamide blends with SURLYN.RTM., polyethylene, ethylene copolymers and EPDM; vinyl and acrylic resins; thermoplastic rubbers such as urethanes, styrene block copolymers, copoly(ether-amides) and olefinic thermoplastic rubbers; and thermoplastic polyesters such as poly(ethylene terephthalate) (hereinafter "PET"), poly(butylene terephthalate) (hereinafter "PBT") and PETG. The reference contains no teaching, however, to use poly(trimethylene terephthalate) (hereinafter "PTT") in a pigmented golf ball cover with an optical brightener. In fact, none of the above disclosures describe the use of poly(trimethylene terephthalate) in golf balls.
Poly(trimethylene terephthalate) has been used mainly in carpet fiber and textile applications. However, similarities in tensile strength, flexural modulus, specific gravity, mold shrinkage, melting point, and glass transition temperature suggest that poly(trimethylene terephthalate) can be a good substitute for polyamides and polyamide blends used in golf ball covers, intermediate layers, and cores.
Co-pending and co-assigned application no. 08/862,831 now U.S. Pat. No. 5,981,654 to Rajagopalgn is directed to compositions and methods for forming golf ball covers, cores and intermediate layers, wherein the composition comprises a blend of a polyamide and poly(trimethylene terephthalate) without optical brightener. The disclosure of that reference, however, contains no teaching or suggestion to formulate a composition without polyamide and with optical brightener.
As a result, a need exists for a golf ball incorporating poly(trimethylene terephthalate) and blends of poly(trimethylene terephthalate), having the feel and spin of balata covered balls and the durability and distance of ionomer covered balls. The present invention provides such a golf ball.